So we want to simplify the expression.
Again there is no equation.
Just so you know assuming we have x>=0
you can write \[\sqrt{18x}=\sqrt{18} \sqrt{x}\]
and you can also do the same for the other terms too.

well, the given answer is
\[3x \sqrt{30} +15x\]
so first I simplified what i could inside the parenthesis and got
\[\sqrt{15x} (3\sqrt{2x} + \sqrt{15x})\]
and then I distributed (Like you said!) and got this
\[3\sqrt{30x ^{2}} + \sqrt{15^{2}x ^{2}}\]
then I canceled out the roots (like you said) and got the answer!